The primary objectives are: 1) to test further the hypothesis that myocardial metabolic activity is uneven between the outer and inner surfaces of the normally functioning left ventricle, 2) to determine the influence of cardiac sympathetic innervation on myocardial metabolic activity, and on the metabolic and collateral blood flow responses to coronary occlusion, and 3) to clarify the physical determinants of myocardial blood flow and its distribution in the left ventricle. To assess regional myocardial metabolic activity individual carbon-14 labeled metabolites will be administered via a coronary cannula to dogs and the animals will be sacrificed at different or optimal times to compare incorporation of carbon-14 into tissue metabolites and carbon dioxide in different layers of the ventricle. To assess the role of cardiac innervation, topically applied phenol will be used to produce a regional sympathectomy of the left ventricle and metabolic conditions in the denervated and innervated regions will be compared. To assess the physical determinants of myocardial blood flow, the main left coronary artery of the dog will be cannulated and, from data on the effects of varying coronary pressure on coronary flow, the coronary closing pressure will be determined and compared at various ventricular filling pressures and coronary venous pressures. Studies on the time to peak flow after release of coronary occlusions of different durations and with different preocclusion coronary pressures will be performed to assess the viscoelastic behavior of the coronary vessels.